This invention generally relates to portable battery-powered equipment. In particular, the invention relates to methods and apparatus for displaying a fuel gauge icon representing the state of a battery in battery-powered equipment.
When providing medical care to patients, it is frequently necessary to monitor the patient using medical diagnostic instruments. One type of instrument, the patient monitor, is capable of monitoring the patient to acquire electrocardiogram data, cardiac output data, respiration data, pulse oximetry data, blood pressure data, temperature data and other parameter data. In particular, lightweight portable monitors exist which can be moved with the patient, allowing continuous monitoring during patient transport.
To facilitate monitoring at remote locations or during patient transport, modern portable patient monitors are powered by rechargeable batteries. Extended-use batteries, with quick recharge times, help maximize monitor availability. Advanced monitors have a smart battery management system which maximizes battery life, reducing maintenance and replacement. Such monitors use smart batteries which can be interrogated to obtain data representing the ongoing state of the battery, e.g., the current charge capacity and battery terminal voltage.
Portable patient monitors with integral battery power supply are commercially available in a compact, ergonomic package which allows easy handling. The compact design is achieved in part through the use of flat display panels. The color or monochrome screen accommodates all numerics and multiple waveforms.
In addition to displaying waveforms and numerics representing the data being acquired, advanced patient monitors are able to display a battery fuel gauge icon representing the current charge capacity of a battery. For example, the battery fuel gauge may display a rectangle of pixels having a width proportional to the percentage of the full charge capacity (assumed to be equal to the design capacity) which remains in the battery. If the full width of the displayed fuel gauge is 75 pixels and the charge remaining is 20% of the full charge capacity, then the current charge state can be depicted by displaying a rectangle on the gauge having a width equal to 15 pixels (i.e., 20% of 75 pixels).
Users of portable battery-powered equipment need to have a dependable means of determining the present condition (state of charge) of the batteries installed in the system. As batteries age, they become chemically worn out and unable to attain their design charge capacity during recharging. In the situation where the full charge capacity is less than the design charge capacity, the system user may think that the remaining run time is greater than what actually remains. The problem posed by the foregoing situation is how to represent the charge level of the battery accurately without misrepresenting the estimated run time remaining. For example, given two batteries that are both reporting that they are full (i.e., unable to take any more charge), one may last one hour and the other may last two hours.
Thus there is a need for a method of informing the system user that the battery, although full, may not last as long as a newer or more recently conditioned or calibrated full battery.
The present invention is a method and an apparatus for informing a system user that the full charge capacity of the battery is less than the design capacity. The preferred embodiment involves adding a layer of detail, namely, the design charge capacity, to the conventional bar graph fuel gauge icon. One horizontal fuel gauge icon for each battery is displayed on the host system display panel. In accordance with the preferred embodiment, the fuel gauge is displayed as three overlapping rectangles which are left justified. The first layer is a dashed outline, always the same width, representing the design charge capacity of the battery. The second layer is a solid outline representing the full charge capacity as a percentage of or in proportion to the design charge capacity. As a battery wears, this level will become a smaller percentage of the full rated capacity indicated by the dashed line. The third layer is a filled rectangle representing the present (actual) charge capacity as a percentage of or in proportion to the full charge capacity.
In accordance with the preferred embodiment, a central processing unit (CPU) of a patient monitor interrogates a microprocessor of a smart battery via a serial data bus to obtain feedback concerning the design, full and current charge capacities of that battery. The charge capacity values are stored in registers in the smart battery microprocessor. Using the polled information, the host system CPU constructs a fuel gauge having indicators representing the respective charge capacities. The newly constructed fuel gauge is then sent to the display controller, which causes the desired fuel gauge icon to be displayed on the display panel.
The invention is preferably implemented completely in software. However, the person skilled in the art will readily appreciate that the invention could also be implemented as hardware or as a dedicated programmable processor. As used in the claims, the term xe2x80x9cfuel gauge processorxe2x80x9d encompasses a CPU programmed with software, hardware or a dedicated programmed processor for performing the fuel gauge display function disclosed herein. The term xe2x80x9cfuel gauge processorxe2x80x9d also encompasses multiple processors having different functions, for example, one processor for processing acquired data representing the charge capacity of a battery and another processor for processing graphical data representing a bar graph fuel gauge for display based on the acquired data.
Furthermore, although the preferred embodiment disclosed herein is incorporated in a battery-powered portable patient monitor, the invention has application in any battery-powered equipment having a processor and a display panel. The invention could even be incorporated into a smart battery pack having a display device, which need only be large enough to display a bar graph fuel gauge icon. Such a smart battery pack would be particularly useful in battery-powered equipment which does not have a display panel.